//go:build ignore

//kage:unit pixels

package main

var Time float

const cloudscale = 0.8
const speed = 0.01
const clouddark = 0.6
const cloudlight = 0.3
const cloudcover = 0.2
const cloudalpha = 8.0
const skytint = 0.5

func rand(co vec2) float {
    return fract(sin(dot(co.xy, vec2(12.9898,-78.233))) * 43758.5453)
}

func hash( p vec2  ) vec2 {
	p = vec2(dot(p,vec2(127.1,311.7)), dot(p,vec2(269.5,183.3)))
	return -1.0 + 2.0*fract(sin(p)*43758.5453123)
}

func noise( p vec2  ) float {
    const K1 = 0.366025404
    const K2 = 0.211324865
	i := floor(p + (p.x+p.y)*K1);	
    a := p - i + (i.x+i.y)*K2

    var o vec2
    if (a.x>a.y) {
      o = vec2(1.0,0.0)
    } else {
      o = vec2(0.0,1.0)
    }

    b := a - o + K2
	c := a - 1.0 + 2.0*K2
    h := max(0.5-vec3(dot(a,a), dot(b,b), dot(c,c) ), 0.0)
	n := h*h*h*h*vec3( dot(a,hash(i+0.0)), dot(b,hash(i+o)), dot(c,hash(i+1.0)))
    return dot(n, vec3(70.0))
}



func fbm(n vec2) float {
    v := n
	total := 0.0
    amplitude := 0.1
	for i := 0; i < 7; i++ {
		total += noise(v) * amplitude
		v = mat2(1.6,  1.2, -1.2,  1.6)  * v
		amplitude *= 0.4
	}
	return total
}

func Fragment(dstPos vec4, srcPos vec2, color vec4) vec4 {
    m := mat2(1.6,  1.2, -1.2,  1.6)
    skycolour1 := vec3(0.45, 0.57, 0.66)
    skycolour2 := vec3(0.55, 0.77, 0.86)

    p := srcPos.xy / imageSrc0Size().xy;
	uv := p*vec2(imageSrc0Size().x/imageSrc0Size().y,1.0);    
    time := Time * speed
    q := fbm(uv * cloudscale * 0.5)

    //ridged noise shape
	r := 0.0
	uv *= cloudscale
    uv.x -= q - time
    weight := 0.8
    for i:=0; i<8; i++{
		r += abs(weight*noise( uv ))
        uv = m*uv + time
		weight *= 0.7
    }

    //noise shape
	f := 0.0
	uv = p*vec2(imageSrc0Size().x/imageSrc0Size().y,1.0);    
	uv *= cloudscale
    uv.x -= q - time
    weight = 0.7
    for i:=0;i<8;i++{
		f += weight*noise( uv )
        uv = m*uv + time
		weight *= 0.6
    }
    
    f *= r + f

    //noise colour
    c := 0.0
    time = Time * speed * 2.0
    uv = p*vec2(imageSrc0Size().x/imageSrc0Size().y,1.0)
	uv *= cloudscale*2.0
    uv.x -= q - time
    weight = 0.4
    for i:=0;i<7;i++{
		c += weight*noise( uv )
        uv = m*uv + time
		weight *= 0.6
    }

    //noise ridge colour
    c1 := 0.0
    time = Time * speed * 3.0
    uv = p*vec2(imageSrc0Size().x/imageSrc0Size().y,1.0)
	uv *= cloudscale*3.0
    uv.x -= q - time
    weight = 0.4
    for i:=0; i<7; i++{
		c1 += abs(weight*noise( uv ))
        uv = m*uv + time
		weight *= 0.6
    }
	
    c += c1

    skycolour := mix(skycolour2, skycolour1, p.y);
    cloudcolour := vec3(1.1, 1.1, 0.9) * clamp((clouddark + cloudlight*c), 0.0, 1.0);
   
    f = cloudcover + cloudalpha*f*r;
    
    result := mix(skycolour, clamp(skytint * skycolour + cloudcolour, 0.0, 1.0), clamp(f + c, 0.0, 1.0));
    
	return vec4( result, 1.0 );
}